An armature of an electric motor is generally provided with a core and a winding wound around the core. The winding is composed of a plurality of wires bundled together, and includes a plurality of coil portions and connecting portions for connecting the coil portions together. The core is provided with a plurality of slots and a plurality of teeth formed between the slots. Here, a single coil portion is provided to a single tooth in an armature structure referred to as a so-called concentrated winding. An example of an armature having a concentrated winding is disclosed in Japanese Laid-open Patent Application No. 2008-109829.
With the stator disclosed in Japanese Laid-open Patent Application No. 2008-109829, an annular core is divided into a plurality of divided cores for each tooth, and two wires are wound around the tooth of the divided cores in regular fashion to form a coil portion. With this armature, the windings are twisted so that the positions of the two wires are reversed between every Nth coil portion so as to satisfy predetermined conditions. The difference in inductance due to nonuniformity of the circumference length formed by each wire is thereby offset and the efficiency of the armature can be improved. Here, the two wires are wound on the tooth in a regular fashion, and the two wires are therefore rotated 180° while remaining parallel and are mutually reversed in position in the portion in which the wires are twisted.
The stator is manufactured in the following manner. First, a single divided core is held in a holding device, and two wires are wound in regular fashion around the divided core being held. The divided core on which the wires have been wound is moved along the axial line in the holding device, and is held in the holding device together with the next divided core. The wires are newly wound around the next divided core 6. This series of steps is carried out in consecutive fashion, whereby a plurality of coil portions are provided to a plurality of divided cores, respectively, and connecting portions for connecting the coil portions are formed in sequential fashion. The divided cores are assembled in an annular shape and secured together to thereby complete an armature.